The present invention relates to a method and apparatus for providing a uniform sound distribution in a confined space, such as in the cabin of an aircraft or of a space craft. Heretofore it was customary to equip aircraft cabins or the like with a relatively high number of individual loudspeakers for maintaining an adequate cabin public address system. However, the sound radiation of loudspeakers is a point type source radiation which means that individual rows of seats will receive a sound saturation which is too loud or too large, whereas other areas in the cabin will not be reached sufficiently. In addition, the arrangement of the special loudspeakers depends on the grouping of the seat rows and requires that openings be cut into the internal wall covering of the cabin.
German Patent Publication (DOS) 1,572,503 discloses a reverberating or echo chamber which is provided with flexible wall components for simulating predetermined sound fields. The wall components are adjustable in their position by special adjustment devices, whereby the outer and inner wall panels of the wall components are flexible. The space between the wall panels is filled with a liquid.
The just described structure is not suitable for aircraft and spacecraft for several reasons. First, the structure is much too expensive. Secondly, the necessary stiffness or rigidity is not available and third, the weight of the cell would be unfeasibly high. German Patent Publication (DOS) 1,572,460 discloses an electronic instrument for the replay of music and speech. The known apparatus comprises a sound wall of synthetic material known as a so-called electro-molecular material. Further, the known apparatus comprises frequency conductors in the shape of sound tubes which are closed relative to the environmental air. This type of structure is also not suitable for aircraft and spacecraft because the manufacturing costs as well as the weight are too large. Besides, it would be necessary to manufacture special elements only for the so-called public address system, whereby the prior art would not be substantially improved.